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My 2011 27 inch iMac will not boot, it plays the startup sound and then freezes on a white screen. I am fairly confident I could fix it myself if I could get it to boot from a USB drive or external disk but holding Option ⌥ during boot does not bring up the boot selector.

Is there another way to get it to boot from a different drive without using Option ⌥?

For example, if I attach an external drive with OS X installed will it automatically boot from it?

edit: I found this page which sounds exactly like what the problem is. So I am looking for another way to replicate what they are accomplishing, by disconnecting the cable, without having to remove the glass.

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Sounds like corrupted firmware. Or boot loader. –  duci9y Sep 15 '12 at 5:55
    
the first step in removing the sata cable is removing the glass panel, so you're out of luck there. have you tried a usb keyboard? ifixit.com/Guide/… –  Ethan Lee Sep 15 '12 at 5:55
    
@duci9y Bootloader I could fix if it would let me pick another drive to boot from. –  Glass Sep 15 '12 at 7:25
    
@ethanlee16 Tried both USB and bluetooth. I need a way to convince it to boot from a different drive, preferably without having to disconnect that cable. I have a USB stick with the Recovery Assistant written to it but no way of getting the iMac to boot from it, but it's starting to look like I'll need some suction cups and a Tork T10. –  Glass Sep 15 '12 at 7:28
    
Then it’s probably corrupted firmware. You will probably need to take it to an Apple Store or Service Provider. –  duci9y Sep 15 '12 at 16:09
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2 Answers

If you could boot OS X, you could use the Startup Disk preference pane to select an alternate boot disk.

There are a few other boot-time options you can try: hold C to boot from an optical disk or hold T to boot into Target Disk mode so you can read the hard drive from another computer (over FireWire or Thunderbolt).

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None of the boot key combos work. Already tried target disk, safe mode (shift), recovery (cmd+r), internet recovery (cmd+opt+r). I used Alt and target disk (T) quite a bit before this happened but now it ignores all of them and goes straight to the white screen. –  Glass Sep 15 '12 at 2:54
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up vote 0 down vote accepted

It seems that there is no way to do this. If holding ALT doesn't work you're out of luck.

Something that may help is disconnecting the main boot drive and connecting another drive with OS X (or a USB stick with the Recovery Assistant on it), and it should boot that by default, but it will not if the default drive is still connected.

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